Scientists
have found clear evidence that water vapor exists in the atmospheres of giant,
hot planets around other stars.
These big
gaseous exoplanets
have masses similar to or greater than Jupiter's (which is about 317.8 times
the mass of Earth). Many of them orbit precariously close to their parent stars,
so they scorching hot.
A team of
astronomers used NASA's Spitzer Space Telescope to examine the spectrum of one
such exoplanet, dubbed HD
189733b, for a telltale signature of water vapor. Water is a key
requirement for life as we know it, though HD 189733b (about 65 light-years
from Earth) is too hot to be habitable.
Models of
the atmospheres of these so called hot Jupiters have predicted that an
abundance of water
vapor should be present in the planets' atmospheres, but recent
observations failed to turn up any conclusive evidence of the molecule's
presence in HD 189733b's atmosphere, said astronomer Drake Deming of NASA's
Goddard Space Flight Center in Greenbelt, Md. Deming was not involved in the
new study.
An April
2007 Astrophysical Journal study reported
to have found strong evidence for water vapor in the atmosphere of a world
called HD209458b using Hubble Space Telescope data. Deming said that this work
"was good evidence" but that "a lot of people [in the scientific
community] had doubts — they didn't think it was unequivocal."
The new
work measured the spectrum of the star/planet system before, during and after the
planet's regular disappearance behind the star, allowing the astronomers to
single out the planet's spectrum. In it, they found "an unequivocal
signature of water vapor in the atmosphere of the brightest transiting
exoplanet yet detected," Deming wrote in an accompanying editorial piece
in Nature.
Nailing
down the technique for the detection of water is a key step toward finding
Earth-like planets that have water and other key life-related molecules, Deming
said.
Last month,
another group of astronomers announced that they had detected
carbon dioxide in HD 189733b's atmosphere; carbon dioxide is one of four
chemicals that life can generate, so it is also a key molecule that could be
used in the search for life outside our own planet.
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